Download Applied Biology DNA structure & replication

DNA –The Language Of Life
Chapter 11
11.1 What is the chemical in
genes?
Computer keyboard analogy.
100+ keys ; it’s all about the order.
Students in the classroom.
Same parts
Same chemicals.
It’s the combination =the many
different characteristics.
Chemicals form DNA.
DNA is the chemical of genes
What does DNA do in cell cycleDNA replicates
DNA divides in mitosis/meiosis.
So every cell has a genetic
blueprint (instructions).
How we know DNA is the genetic material:
Griffith’s ExperimentsIdentified a Transforming Factor.
2 Strains of pneumonia bacteria.
Smooth strain- capsule.
–Causes pneumonia in mice.
Rough strain - no capsule.
–Does not cause pneumonia.
Heat killed smooth strain.
Does not cause pneumonia.
Combined heat-killed smooth strain
and rough strain bacteria.
Caused disease in mice .
Griffith’s Experiment
Figure 11-1 Griffith showed that although a deadly strain of bacteria could be
made harmless by heating it, some factor in that strain is still able to change
other harmless bacteria into deadly ones. He called this the "transforming
factor."
What happened?
The Rough strain was transformed
to become smooth.
All descendents of the transformed
bacteria were smooth &caused
disease.
Griffith called the substance
“transforming factor”.
Further Experimentsidentify the transforming factor
Chromosomes are made up of
proteins and DNA.
Is the factor DNA or Protein?
Most scientists then-thought the
hereditary material was protein not
DNA.
Avery’s Experiment
Avery used different enzymes.
Protein destroying enzymes were used on
Griffith’s heat treated and live rough mixture.
Result- bacteria were transformed.
Protein was not transforming factor.
DNA destroying enzymes were used.
Result- bacteria were not transformed.
So….
DNA was the transforming factor.
Hershey and ChaseBacteriophage Experiment
Hershey & Chase’s
Bacteriophage Experiment
DNA is the genetic material
Viruses are not cells.
DNA wrapped in a protein coat.
Only reproduce in a living cell.
Viral genetic material directs host cell to
make more virus.
Bacteriophage -viruses that attack
bacteria..
outer coat of protein
inner core of DNA.
Radioactive sulfur labels protein coat.
Radioactive phosphorous labels DNA.
When phage protein coats are labeled,
radioactivity was outside of the cell.
When phage DNA is labeled
radioactivity is inside the cell.
Conclusion :
phage DNA enters bacterial cell , NOT protein.
So- DNA is the genetic material !
11.2 Structure of DNA
pp 229-231
Nucleic AcidsFunction - store and transfer genetic
information. Genes are made of DNA.
Nucleic Acids- made up of many units of
nucleotides(monomers)
Nucleotides are the building blocks.
DNA- Deoxyribonucleic Acid
4 different nucleotides.
A=adenine
G=guanine
C=cytosine
T=thymine
NUCLEOTIDE STRUCTURE
3 PARTS OF A NUCLEOTIDE:
1.
2.
3.
Deoxyribose - 5 Carbon sugar
Phosphate Group- Phosphorous
atom with 4 atoms of oxygen
Nitrogen base.
Single ring-pyrimidine
Double rings-purines
The 4 nucleotides of DNA:
The nitrogenous base is the difference.
Pyrimidines- single-ring structures.
Thymine- T.
Cytosine- C.
Purines- double-ring structures.
Adenine- A.
Guanine- G.
The letters T,C,A,G are used to represent
the bases and also the nucleotides that
contain them.
Sugar-phosphate DNA backbone
Double helix (ladder )model
Outside of the ladder
Repeating pattern
Sugar of one nucleotide is connected to
the phosphate group of the next.
Attached nitrogen bases are on the
inside (rungs)of the double helix
model.
Nucleotide chains can vary in length.
Nucleotides can combine in many different
sequences represented by the letter symbols.
CTAGCCTTGAC
Nitrogenous Base Pairing:
A=T ( by 2 hydrogen bonds)
G=C (by 3 hydrogen bonds)
Called Complimentary Base Pairing.
Base-pairing rule- each base must pair up with its
complementary base.
Double Helix Structure
1950s- Franklin- X-ray crystallography.
Showed basic shape to be a helix
1953- Watson and Crick model
Used Franklin’s photos
Twisting shape-double helix ; 2 nucleotides
twist around each other.
Sugar-phosphate backbone on outside
Nitrogenous bases on the inside joined by
hydrogen bonds.
11.3 DNA Replication-the process of
copying a DNA molecule.
Template mechanism
1.The 2 strands of the double helix
separate.
DNA helicase (enzyme) “unzips” the DNA,
breaking the hydrogen bonds between the
base pairs.
Each strand is template for a new,
complementary strand to form.
Base-pairing rules are followed.
A-T
G-C
DNA Replication Continued
2. DNA polymerase (enzyme)
“glues” the bonds between the nucleotides of
the new DNA strand.
“proof-reads” new DNA.
DNA replication begins at specific sites
called points of origin.
Replication (copying) proceeds in an
outward directions from the points of origin
resulting in replicating bubbles.
The parent DNA strands open up as new
daughter strands grow.
Result of DNA replication:
Result- 2 double stranded DNA
molecules;
one old & one complementary new
strand.
DNA replication occurs before a cell
divides.
In what stage of the cell cycle?